1. Field of the Invention
The present invention relates to a photosensitive resin composition suitable to a photolithography using an activating radiation such as a far ultraviolet ray, an electron beam, an ion beam and an X-ray in a semiconductor manufacturing process, and a patterning method using the same.
2. Description of Related Art
In the manufacturing of various semiconductor devices typified by a dynamic random access memory (DRAM), the demand for elevation of the density and the integration of the device is now increased more and more. In order to fulfill this demand, it is indispensable to microminiaturize the pattern. Therefore, the request for the photolithography is now becoming severe more and more.
One means for microminiaturizing the pattern is to shorten the wave length of an exposing light used in the patterning. At present, the manufacturing of DRAMs having the integration degree of not less than 1 G bits (patterning size of not larger than 0.2 xcexcm) requires a fine patterning, which requires a light source having a short wavelength. The photolithography using an ArF excimer laser (wavelength is 193 nm) is now actively researched.
A resist material, which is a pattern forming material used in this fine patterning, is required to have high sensitivity in addition to a high resolution corresponding to the size of the fine patterning. The reason for this is that, in order to reduce a damage to optical members such as lens in an exposure machine, it is necessary to form a desired pattern with a relatively low exposure amount. In addition, particularly when the exposure light source such as the excimer laser is used, since the life of the gas which is a laser oscillation material is short, and since the laser apparatus is expensive, it is necessary to elevate the cost performance of the laser.
As a method for enhancing the sensitivity of the resist, there is used a chemically amplified resist using a photo acid generating agent such as a photo cation generating agent, which generates acid in response to exposure of the activating radiation, as a photosensitive agent. For example, Japanese Patent Application Postexamination Publication No. JP-B-02-027660 discloses a resist composed of a combination of triphenylsulfoniumhexafluoroaresenate and poly(p-ter-butoxycarbonyloxy-xcex1-methylstrene. The chemically amplified resist is characterized in that the photo acid generating agent, which is a material included in the photo acid generating agent and generating acid in response to the light radiation, generates a proton acid, and with a heating treatment after the exposure, the proton acid thus generated is caused to move in a resist solid state, to amplify a chemical reaction of the resist resin by a catalytic reaction up to hundreds times to thousands times. Thus, a remarkably high sensitivity can be attained in comparison with the prior art having the optical reaction efficiency (reaction per one photon) of smaller than 1 (one). At present, most of newly developed resist is a chemical amplified resist, and a chemical amplification mechanism has to be adopted in developing a high sensitive material meeting with a shortened wavelength of the exposure light source.
In the prior art lithography technique using an exposure light having the wavelength longer than that of an KrF excimer laser (248 nm), the photosensitive resin composition includes the resin component typified by a resin, such as a novolak resin and poly(p-vinylphenol), containing an aromatic ring in unit structures. However, the light absorption by the aromatic ring of the light having the wavelength of not greater than 220 nm is extremely strong, and therefore, these prior art resins cannot be used as they are, for the exposure light having the wavelength of not greater than 220 nm. (Namely, a major portion of the exposure light is absorbed at a surface of the resist, so that the exposure light does not reach a substrate, with the result that a fine patterning of the resist cannot be attained) (Sasago et al xe2x80x9cArF excimer laser lithography (3) xe2x80x94Evaluation of Resistxe2x80x94xe2x80x9d, 36th Applied Physics Institution Conference Manuscripts, 1p-K-4, 1989). Therefore, a resin material having no aromatic ring but having an etching resistance is required.
For example, as a polymer having a transparency to the light having the wavelength of 193 nm and a dry etching resistance, there are proposed a copolymer having adamantylmethacrylate units which are alicyclic polymer (S. Takechi et al, Journal of Photopolymer Science and Technology, Vol. 5, No. 3, pp439-446, 1992, and Japanese Patent Application Pre-examination Publication No. JP-A-05-265212), a poly(norbornylmethacrylate (M. Endo et al, Proceedings of IEDM, CA14-18, 1992 (San Francisco)), a copolymer having isobornylmethacrylate units (G. M. Wallraff et al, Journal of Vacuum Science and Technology, B11(6), pp2783-2788, 1993), and a copolymer having poly(menthylmethacrylate) units (Japanese Patent Application Pre-examination Publication No. JP-A-08-08-2925). Furthermore, the co-inventors of this application proposes a polymer having a transparency to the light having the wavelength of not greater than 200 nm and a dry etching resistance and also having a difference in solubility between a pre-exposure and a post-exposure, and a photosensitive resin composition using the same (Japanese Patent Application Pre-examination Publication No. JP-A-08-259626). In addition, a 0.16 xcexcm line-and-space pattern was formed on this photosensitive resin by using a ArF excimer laser experimental machine (Nikon lens, numerical aperture=0.6) (K. Maeda et a, Proceedings of SPIE, Vol.2724, pp377-395).
However, all of the above mentioned resist materials are a positive resist, and no negative resist of chemical amplification type for an ArF excimer laser exposure has yet been reported. In a future development of DRAMs, it is required to develop a negative resist on a rush basis The background of requiring the negative resist is that a recent elevated expectation of a multimedia information society needs a DRAM having a large capacity and a high operation speed, with the result that it is considered to be of necessity to install the DRAM and a logic circuit on the same single chip so as to realize a high speed operation and a high performance. Namely, since the negative resist is more advantageous than the positive resist, in a forming of an isolated pattern, it is indispensable to form the logic pattern. Furthermore, in the lithography in the process of manufacturing a DRAM of 1 giga bits or more, use of a phase shift mask is indispensable, and a phase shift mask can be easily formed in the negative resist, in comparison with the positive resist. As mentioned above, the negative resist is required more and more in future. However, as mentioned above, there is no report of the negative resist having a high transparency to the light having the wavelength of 193 nm and a high resolution, and an early development is required. Many negative resists meeting with the KrF excimer laser having wavelength of 193 nm have been reported and developed, however, since those negative resists include an unsaturated bond such as an aromatic ring in the resin and a crosslinking agent, those negative resists are not transparent to the light having the wavelength of 193 nm which is the wavelength of the ArF excinier laser, and therefore, cannot be used.
Accordingly, the present invention has an object to provide a sensitive resin composition which has a high transparency to the light in a far ultraviolet region and a high sensitivity and a high resolution to an exposure light of a far ultraviolet ray.
The present invention also has an object to provide a sensitive resin composition suitable to a negative photoresist using the ArF excimer laser as an exposure light.
Furthermore, the present invention has an object to provide a patterning method capable of forming a fine pattern necessary for a semiconductor manufacturing.
The co-inventors found out that the above mentioned objects can be achieved by the sensitive resin composition and patterning method which will be described in the following, and invented the present invention.
The sensitive resin composition in accordance with the present invention has a 75 to 99.8 weight part of polymer having repetition units expressed by a general formula (1): 
where R1, R3 and R5, represent one of a hydrogen atom and a methyl group, R2 represents a bridged cyclic hydrocarbon group having a carbon number in the range of 7 to 22 inclusive, R4 represents a hydrocarbon group including an epoxy group, x+y+z=1, wherein 0 less than xxe2x89xa60.7, 0xe2x89xa6y less than 1, 0 less than zxe2x89xa61), and the polymer has a weight averaged molecular weight of 1,000 to 500,000, and 0.2 to 25 weight part of photo acid generator
Furthermore, the sensitive resin composition in accordance with the present invention has a 75 to 99.8 weight part of polymer having repetition units expressed by a general formula (1): 
where R1, R3, and R5 represent one of a hydrogen atom and a methyl group, R2 represents a bridged cyclic hydrocarbon group having a carbon number in the range of 7 to 22 inclusive, R4 represents a hydrocarbon group including an epoxy group, x+y+z=1, wherein 0 less than xxe2x89xa60.7, 0xe2x89xa6y less than 1, 0 less than zxe2x89xa61), and the polymer has a weight averaged molecular weight of 1,000 to 500,000, and 0.2 to 25 weight part of photo acid generator, and a multi-functional epoxy compound of 0.5 to 60 weight parts per 100 parts of the whole composition including the multi-functional epoxy compound itself.
Furthermore, the patterning method in accordance with the present invention is characterized by depositing the sensitive resin composition in accordance with the present invention on a substrate to be worked, and heating it, and thereafter, exposing it to an activating light, conducting a heat treatment, developing it so as to form a pattern.
In the sensitive resin composition in accordance with the present invention, an aliphatic hydrocarbon residue is introduced in the repetition units of the polymer, so that the transparency to the light having the wavelength of 180 nm to 248 nm and an etching resistance is given, and the epoxy group is introduced in the repetition units of the polymer, and if necessary, the multifunctional epoxy compound is included, so that a crosslinking reaction occurs due to an acid generated by the exposure.